Protective cover and bearing device including protective cover

ABSTRACT

The present invention is intended to provide a protective cover, comprising an inner ring  12  with an inner ring track surface  12 A on an outer peripheral surface; an outer ring  13  with an outer ring track surface  13 A on an inner peripheral surface; a bearing with rolling elements  14  between the inner ring track surface  12 A and the outer ring track surface  13 A; a magnetic encoder  8  that is positioned at one axial end portion of the bearing and fixed to the inner ring  12 ; and a magnetic sensor that is fixed to the outer ring  13 , a cup-shaped protective cover  1  press-fitted into the outer ring  13  to cover the magnetic encoder  8  and intervene between the magnetic encoder  8  and the magnetic sensor is formed by performing cold press molding of an austenitic stainless steel plate material with a nickel content of 8.5 to 13 weight %.

TECHNICAL FIELD

The present invention relates to a cup-shaped protective cover that ispress-fitted into an outer ring of a bearing to cover a magneticencoder, and a bearing device including the protective cover.

BACKGROUND ART

The antilock brake system (ABS) for use in efficient and safety brakingwithout locking of wheels of automobiles was included in 45% ofautomobiles produced in Japan in 1996, and in more than 90% in 2009. Atpresent, the antilock brake system is included in most of automobiles.

The widespread antilock brake system is intended, for example, to detectthe rotation speeds of wheels by a rotation speed detector (wheel speedsensor), calculate the acceleration and the deceleration and estimatethe vehicle speed and the slip ratio by a controller, and drive anactuator to control the brake fluid pressure based on the calculationand estimation results.

Bearing device with such a rotation speed detector in a roll bearing forsupporting automobile wheels (hub bearing) is also widely used. There isa bearing device structured such that a seal member is fitted to theinner side of opposed surfaces of a rotational inner ring and a fixedouter ring, a magnetic encoder with N and S poles alternately arrangedat regular intervals in the circumferential direction is attached to theinner ring at the inner side of the seal member, and a magnetic sensoris attached to the outer ring so as to be opposed to the magneticencoder to detect the rotation of the magnetic encoder (for example,refer to Patent Document 1).

In the structure of the bearing device as described in Patent Document1, muddy water or magnetized iron pieces may enter between the magneticencoder and the magnetic sensor, which causes damage to the magneticencoder and the magnetic sensor or changes in magnetic property of themagnetic encoder. In addition, the rotation torque of the bearing deviceincreases due to sliding resistance of the seal member positioned at theouter side of the magnetic encoder.

To solve these problems, there is a bearing device in which a cup-shapedprotective cover is press-fitted into the inner end portion of the outerring to cover the magnetic encoder from the inner side without the sealmember (for example, refer to Patent Document 2).

CITATION LIST Patent Literatures

Patent Document 1: JP-A No. 2005-241351

Patent Document 2: JP-A No. 2011-084265

SUMMARY OF INVENTION Technical Problem

According to Patent Document 2, the magnetic force of the magneticencoder needs to penetrate through the protective cover and reach themagnetic sensor, and thus the protective cover is to be non-magnetic andcorrosion-resistive. Accordingly, the material for the protective coveris generally an austenitic stainless steel SUS304 containingchrome-nickel as a main component. The protective cover is generallyformed by performing press molding of a SUS304 plate material.

The inventor of the subject application has produced a protective coverof a desired shape by performing cold press molding of ageneral-composition SUS304 plate material and has found that a largepart of the plate material changed from austenite to martensite due todeformation-induced martensitic transformation.

The martensite structure has the property of being magnetized. When theprotective cover with a large part having undergone deformation-inducedmartensitic transformation is used, the protective cover may disturb amagnetic field between the magnetic encoder and the magnetic sensor toexert an adverse effect on detection accuracy.

The part having undergone deformation-induced martensitic transformationcan be returned to austenite by solution treatment (solution heattreatment). However, the execution of solution treatment leads to costincrease and may cause dimension changes due to heating.

Accordingly, it is desired to use an austenitic stainless steel platefor the protective cover without any portion having undergonedeformation-induced martensitic transformation or with a small portionhaving undergone deformation-induced martensitic transformation when thecup-shaped protective cover is formed by performing cold press moldingof the material.

In view of the foregoing circumstances, an object of the presentinvention is to provide a protective cover that is less magnetized andis likely to satisfy required specifications for residual magneticproperty when the protective cover is formed by performing cold pressmolding of an austenitic stainless steel plate material.

Solution to Problem

The inventor of the subject application has earnestly studied anaustenitic stainless steel material including chrome nickel as a maincomponent, taking notice of a nickel content relative to the totalweight. Then, the inventor has tried to produce a cup-shaped protectivecover sufficiently satisfying required specifications for residualmagnetic property through cold press molding while suppressing thecontent of nickel as an expensive metal but making the content of nickelhigher than the general content of nickel in a commercially suppliedSUS304. Then, the inventor has evaluated and examined the residualmagnetic property of the protective cover after the press molding,thereby completing the present invention.

Specifically, to solve the foregoing problems, the protective coveraccording to the present invention is a cup-shaped protective cover fora bearing device including: an inner ring with an inner ring tracksurface on an outer peripheral surface; an outer ring with an outer ringtrack surface on an inner peripheral surface; a bearing with a rollingelement between the inner ring track surface and the outer ring tracksurface; a magnetic encoder that is positioned at one axial end portionof the bearing, fixed to the inner ring, and has N and S polesalternately arranged at regular intervals in the circumferentialdirection; and a magnetic sensor that is fixed to the outer ring so asto be opposed to the magnetic poles of the magnetic encoder to detectthe rotation of the magnetic encoder, wherein the protective cover ispress-fitted into the outer ring to cover the magnetic encoder andintervene between the magnetic encoder and the magnetic sensor, and theprotective cover is formed by performing cold press molding of anaustenitic stainless steel plate material with a nickel content of 8.5to 13 weight %.

According to this configuration, the protective cover is formed byperforming cold press molding of an austenitic stainless steel platematerial with a nickel content of 8.5 to 13 weight %, and thus theresidual flux density of nickel in the material (austenitic stainlesssteel) for the cold-pressed protective cover is significantly lower thanthat in the case of using a SUS304 with a general nickel content (about8 weight %).

Accordingly, the cold-pressed protective cover is hardly magnetized andis likely to satisfy the required specifications for residual magneticproperty.

In addition, since the protective cover is not subjected to solutiontreatment, it is possible to prevent increase in manufacturing costs anddimension changes due to heating to improve the yield of products.

The bearing device according to the present invention includes theprotective cover.

Advantageous Effects of Invention

According to the present invention, the protective cover and the bearingdevice including the protective cover produce significant advantagesthat the cold-pressed protective cover has a low residual flux density,and thus is hardly magnetized and is likely to satisfy the requiredspecifications for residual magnetic property.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a vertical cross-sectional view of a bearing device with aprotective cover according to an embodiment of the present invention;

FIG. 2 is an enlarged vertical cross-sectional view of main parts of thesame;

FIGS. 3( a) and (b) illustrate the protective cover according to theembodiment of the present invention: FIG. 3( a) is a verticalcross-sectional view; and FIG. 3( b) is a perspective view;

FIG. 4 is a front view of a configuration example of an experimentdevice that measures the residual flux density of a sensing surface ofthe protective cover; and

FIG. 5 is a graph showing the relationship between the nickel contentsand the residual flux densities in Table 1.

DESCRIPTION OF EMBODIMENTS

Embodiment of the present invention will be described below in detailwith reference to the accompanying drawings. However, the presentinvention is not limited to the embodiment illustrated in theaccompanying drawings but includes all of embodiments satisfyingrequirements described in the claims.

As illustrated in the vertical cross-sectional view of FIG. 1 and theenlarged vertical cross-sectional view of main parts of FIG. 2, abearing device 11 according to the embodiment of the present inventionincludes: a bearing having an inner ring 12 with an inner ring tracksurface 12A on an outer peripheral surface, an outer ring 13 with anouter ring track surface 13A on an inner peripheral surface, and rollingelements 14, 14, . . . between the inner ring track surface 12A and theouter ring track surface 13A; a magnetic encoder 8 that is positioned atone axial end portion of the bearing and fixed to the inner ring 12; amagnetic sensor 10 that is fixed to the outer ring 13 and opposed tomagnetic poles of the magnetic encoder 8 to detect rotation of themagnetic encoder 8; a cup-shaped protective cover 1 that is press-fittedinto the outer ring 13 to cover the magnetic encoder 8 and intervenebetween the magnetic encoder 8 and the magnetic sensor 10; and a sealmember 15 that is arranged at the other axial end portion of thebearing, and the like.

The inside of the bearing is sealed by the protective cover 1 and theseal member 15 at the both axial end portions of the bearing, and themagnetic encoder 8 is accommodated in the inner space of the bearing.This allows the magnetic encoder 8 and the inside of the bearing to beprotected from foreign matter or the like.

The magnetic encoder 8 attached to the rotational inner ring 12 andhaving N and S poles alternately arranged at regular intervals in thecircumferential direction and the magnetic sensor 10 attached to thefixed outer ring 13 constitute a rotation speed detector.

A support member 9 is composed of a cylindrical part 9A and an annularpart 9B extended radially outward from the end edge of the cylindricalpart 9A. The magnetic encoder 8 having N and S poles alternatelyarranged at regular intervals in the circumferential direction is fixedto the annular part 9B.

When the cylindrical part 9A is externally fitted to the inner ring 12,the magnetic encoder 8 is fixed to the inner ring 12 via the supportmember 9 to rotate the magnetic encoder 8 integrally with the inner ring12.

As illustrated in the vertical cross-sectional view of FIG. 3( a) andthe perspective view of FIG. 3( b), the protective cover 1 according tothe embodiment of the present invention includes: a first cylindricalpart 2 press-fitted into the outer ring 13 (refer to FIGS. 1 and 2); asecond cylindrical part 3 smaller in diameter than the first cylindricalpart 2 and connected to an end edge of the first cylindrical part 2; anannular part 4 connected to an end edge of the second cylindrical part 3and extended radially inward; a third cylindrical part 5 connected to aninner diameter-side end edge of the cylindrical part 4 and extended inthe axial direction; a disc part 6 connected to an end edge of the thirdcylindrical part 5; and a seal body 7 vulcanized and adhered to theouter peripheral surface of the second cylindrical part 3. A recess 6Ais formed in the center of the disc part 6.

The base part of the protective cover 1 (except for the seal body 7) isformed by performing press molding of an austenitic stainless steelplate material with a nickel content of 8.5 to 13 weight %.

The seal body 7 is an elastic body such as synthetic rubber to improveairtightness between the protective cover 1 and the outer ring 13. Theseal body 7 may be made from one of oil-resistant favorable rubbermaterials such as nitrile rubber (NBR), hydrogenated nitrile rubber(HNBR), acrylic rubber (ACM), ethylene-acrylic rubber (AEM), fluorinerubber (FKM, FPM), and silicone rubber (VQM), or a blend of two or moreof the same.

Further, the surface of the plate material for the base part of theprotective cover 1 is dull-finished. This makes working oil likely to beretained at the press molding and prevents baking at the drawingprocess. Accordingly, scratches on the surface of the protective cover 1are less prominent, and the matted surface improves the appearance ofthe protective cover 1 and the adhesion of the seal body 7.

[Evaluation of Residual Magnetic Property]

Next, descriptions will be given as to experiments on the protectivecover 1 formed by performing cold press molding of a material with ahigher nickel content than a general nickel content (about 8% of thetotal weight) of a commercially supplied SUS304 for evaluation ofresidual magnetic property.

Experimental Method

(1) First, the protective cover 1 formed by performing cold pressmolding of an austenitic stainless steel plate material was stored in amagnetization coil (air core coil with a diameter of 100 mm produced byMagnet Force Co., Ltd). A saturation magnetic field was applied to theprotective cover 1 by a magnetizing electric power supply (oilcondenser-type magnetizing electric power supply MFC-1510 produced byMagnet Force Co., Ltd).

(2) Next, the protective cover 1 with the saturation magnetic field wasfixed on a turning table 16 in axial alignment with each other, asillustrated in the front view of a configuration example of anexperiment device of FIG. 4. A probe (axial probe MSA-410 produced byToyo Corporation) supported by a support instrument 17 was arranged soas to be axially opposed to the sensing surface of the protective cover1 with a gap of 0.5 mm therebetween in the height direction. A teslameter (410-type handy gauss meter produced by Toyo Corporation) was usedto measure the maximum value of the residual flux density of theprotective cover 1 while the turning table 16 was turned.

EXAMPLES

As examples 1 to 3, commercially supplied austenitic stainless steelplate materials of the following steel grades were selected:

Example 1

Of JIS-based SUS304 materials with a nickel content of 8.00 to 10.50%relative to the total weight, a SUS304 with a nickel content of 8.79%was used.

Example 2

Of JIS-based SUS304L materials with a nickel content of 9.00 to 13.00%relative to the total weight, a SUS304L with a nickel content of 10.05%was used.

Example 3

Of JIS-based SUS316L materials with a nickel content of 12.00 to 15.00%relative to the total weight, a SUS316L with a nickel content of 12.17%was used.

COMPARATIVE EXAMPLES

As comparative examples 1 and 2, commercially supplied austeniticstainless steel plate materials of the following steel grades wereselected:

Comparative Example 1

Of JIS-based SUS304 materials with a nickel content of 8.00 to 10.50%relative to the total weight, a SUS304 with a nickel content of 8.06%was used.

Comparative Example 2

Of JIS-based SUS304J2 materials with a nickel content of 6.00 to 9.00%relative to the total weight, a SUS304J2 with a nickel content of 6.67%was used.

Experimental Results and Considerations

Table 1 shows the measured maximum values of residual flux densities ofthe austenitic stainless steel protective covers of the examples 1 to 3and the comparative examples 1 and 2. FIG. 5 illustrates therelationship between the nickel contents and the residual flux densitiesin Table 1.

TABLE 1 Example/Comparative example Comparative Comparative Example 1Example 2 Example 3 Example 1 Example 2 Material (JIS steel grade)SUS304 SUS304L SUS316L SUS304 SUS304J2 Nickel content (weight %) 8.7910.05 12.17 8.06 6.67 Residual flux density (mT) 0.11 0.04 0.03 0.200.21

It is understood from FIG. 5 that the austenitic stainless steelprotective covers with relatively low nickel contents as the comparativeexamples 1 and 2 are larger in the measured maximum values of residualflux density, and the austenitic stainless steel protective covers withnickel contents of 8.5 weight % or more are smaller in the measuredmaximum values of residual flux density. In particular, it is noted thatthe austenitic stainless steel protective covers with nickel contents of10 weight % or more are significantly smaller in the measured maximumvalues of residual flux density.

For example, the austenitic stainless steel protective cover with anickel content of 10.05 weight % in the example 2 has the measuredmaximum value of residual flux density of 0.04 mT, and the austeniticstainless steel protective cover with a nickel content of 8.06 weight %in the comparative example 1 has the measured maximum value of residualflux density of 0.20 mT.

Accordingly, it is understood that, as compared to the comparativeexample 1 with the lower nickel content, the example 2 with the highernickel content has a significant smaller measured value of residual fluxdensity that is ⅕ of that of the comparative example 1, and the example2 is thus less magnetized.

In addition, the same measurement was performed on a part other than thesensing surface (for example, the first cylindrical part 2 illustratedin FIG. 2), which revealed that the examples are significantly smallerin residual flux density than the comparative examples similar to thecase of the sensing surface.

As described above, the content of nickel in an austenitic stainlesssteel plate material for cold press molding of a protective cover ismore preferably 10 weight % or more from the viewpoint of making theprotective cover less magnetized to satisfy required specifications forresidual magnetic property, and is preferably 8.5 weight % or more fromthe viewpoint of making the protective cover less magnetized andsuppressing the content of expensive nickel as much as possible.

Nickel is an expensive material and therefore the upper limit of anickel content is preferably 13 weight % or less from the viewpoint ofsuppressing a nickel content and reducing manufacturing costs.

The material with a nickel content of 8.5 to 13 weight % may bepreferably a SUS304 with a nickel content of 8.5 weight % or more as inthe example 1, the SUS304L, the SUS316L, a JIS-based SUS305 with anickel content of 10.50 to 13.00 weight % relative to the total weight,a SUS321 with a nickel content of 9.00 to 13.00 weight %, or a SUS347with a nickel content of 9.00 to 13.00 weight %.

The protective cover 1 according to the embodiment of the presentinvention as described above is formed by performing cold press moldingof an austenitic stainless steel plate material with a nickel content of8.5 to 13 weight %. Therefore, the material for the protective cover 1(austenitic stainless steel) is significantly smaller in residual fluxdensity than the SUS304 with a general nickel content (about 8 weight%).

Accordingly, when being formed by cold press molding, the protectivecover 1 is extremely less magnetized and is likely to satisfy requiredspecifications for residual magnetic property.

In addition, since the protective cover 1 is not subjected to solutiontreatment, it is possible to prevent increase in manufacturing costinvolved in the treatment and dimension changes due to heating, therebyimproving the yield of the protective cover 1.

REFERENCE SIGNS LIST

-   1 Protective cover-   2 First cylindrical part-   3 Second cylindrical part-   4 Annular part-   5 Third cylindrical part-   6 Disc part-   6A Recess-   7 Seal body-   8 Magnetic encoder-   9 Support member-   9A Cylindrical part-   9B Annular part-   10 Magnetic sensor-   11 Bearing device-   12 Inner ring-   12A Inner ring track surface-   13 Outer ring-   13A Outer ring track surface-   14 Rolling element-   15 Seal member-   16 Turning table-   17 Support instrument-   18 Probe

1. A cup-shaped protective cover for a bearing device including: aninner ring with an inner ring track surface on an outer peripheralsurface; an outer ring with an outer ring track surface on an innerperipheral surface; a bearing with a rolling element between the innerring track surface and the outer ring track surface; a magnetic encoderthat is positioned at one axial end portion of the bearing, fixed to theinner ring, and has N and S poles alternately arranged at regularintervals in the circumferential direction; and a magnetic sensor thatis fixed to the outer ring so as to be opposed to the magnetic poles ofthe magnetic encoder to detect the rotation of the magnetic encoder, theprotective cover being press-fitted into the outer ring to cover themagnetic encoder and intervene between the magnetic encoder and themagnetic sensor, wherein the protective cover is formed by performingcold press molding of an austenitic stainless steel plate material witha nickel content of 8.5 to 13 weight %.
 2. A bearing device comprisingthe protective cover according to claim 1.